I was hoping to buy a Mesa Boogie Thiele guitar cabinet, but the price blew me away! So after weeks of searching, I found plans for a very similar cab.
The Mesa Thiele and the EV (ElectroVoice) TL806 are almost exactly the same. Many people on forums that i browsed through believe Mesa copied EV's plans for the Thiele. (They are open sourced, so it doesn't matter anyway)
The only major difference is that Mesa switched a few dimensions on their cab so it would have a flush fit under the Mark III amp head. But they maintained the internal volume of 1.3 ft, which is the most critical part.
I will be building mine with an extension on each side so it fits under my Peavey 5150, but i will not be changing any dimensions! Just adding two extra "enclosures". They were my idea, but feel free to use them, or discard them. *If you use them, be sure you make them the width of your amp head!!!* (the 5150 is relatively small compared to marshalls)
Enough words! get started! (after you read the whole thing of course.....)